a step S1: selecting a depleted oil and gas reservoir suitable for the biochemical conversion of carbon dioxide as a target depleted oil and gas reservoir;

a step S2: adjusting a temperature of the target depleted oil and gas reservoir to 30° C. to 70° C. and detecting whether formation water of the target depleted oil and gas reservoir contains methanogenic archaea, wherein in response to the target depleted oil and gas reservoir not containing the methanogenic archaea, injecting the methanogenic archaea into the target depleted oil and gas reservoir, and then performing a step S3, and in response to the target depleted oil and gas reservoir containing the methanogenic archaea, proceeding directly to the step S3;

the step S3: injecting a mixture of carbon dioxide and hydrogen into the target depleted oil and gas reservoir through a gas injection well;

step S4: shutting down the gas injection well for half a year to one year to wait for the methanogenic archaea to convert the carbon dioxide and hydrogen in the target depleted oil and gas reservoir into methane and exploiting methane and heat energy in the target depleted oil and gas reservoir;

wherein:

a structure of the target depleted oil and gas reservoir in the step S1 is an anticline or a fault with a porosity greater than 10%, a permeability greater than 10 mD, a water saturation greater than 10%, and a mineralization of the formation water less than 150 g/L with a pH value being in a range of 6.4 to 7.5; and

a specific method of adjusting the temperature of the target depleted oil and gas reservoir to 30° C. to 70° C. in the step S2 comprises injecting pre-fluid into the target depleted oil and gas reservoir so that the temperature of the target depleted oil and gas reservoir drops to 30° C. to 70° C. in response to the temperature of the target depleted oil and gas reservoir being higher than 70° C.